POLYMERIC ORGANOSILICON SYSTEMS .15. THERMAL AND RADICAL-INDUCED POLYMERIZATION OF 1,2,5,6-TETRASILACYCLOOCTA-3,7-DIYNES

Treatment of 1,2,5,6-tetramethyl-1,2,5,6-tetraphenyl-, 1,2,5,6-tetrabutyl-1,2,5,6-tetramethyl-, 1,2,5,6-tetrahexyl-1,2,5,6-tetramethyl-, 1,1,2,2,5,5,6,6-octaethyl-, and 1,1,2,2,5,5,6,6-octabutyl-1,2,5,6-tetrasilacycloocta-3,7-diyne (la-le) in a degassed tube at 230-degrees-C afforded the respective ring-opened polymers, poly[(disilanylene)ethynylenes] (2a-2e) with high molecular weights in high yields. In the presence of a catalytic amount of di-tert-butyl peroxide (DTBP), the tetrasilacyclooctadiynes also undergo polymerization to give the ring-opened polymers at a lower temperature than the thermal ring-opening polymerization. Heating la with 5 mol % of DTBP at 150-degrees-C for 5 h gave 2a whose molecular weight was determined to be 25 000 in 60 % yield, while 1d afforded 2d with a molecular weight of 159 000 in 63 % yield. Similar treatment of 1b and le at 180-degrees-C produced polymers 2b and 2e with molecular weights of 28 000 and 7000, respectively. The reaction of tetrasilacyclooctadiynes with a catalytic amount of DTBP in the presence of a hydrosilane afforded ring-opened polymers in yields higher than those of polymers obtained in the absence of the hydrosilane. Treatment of 2d, whose molecular weight was determined to be 157 000, with 6 mol % DTBP and 19 mol % methyldiphenylsilane at 150-degrees-C for 5 h resulted in depolymerization of the starting polymer to give the polymer with a molecular weight of 12 000 in quantitative yield.